Anodizing is a well-known electrochemical process that changes the raw outer surface of a metal part (typically aluminum) into a metal oxide coating. The metal oxide coating is very hard compared to the base metal, and is generally very thin. Moreover, the oxide coating is relatively porous, and for that reason is capable of accepting a variety of dyes and inks that can add color and even images to the metallic surface.
There are several known methods for applying multicolor images to anodized surfaces, commonly aluminum parts and manufactured aluminum goods such as lighters, knives, and virtually any other aluminum item. Some of the known methods call for modifications to the anodizing process to modify the oxide coating on the outer surface of the part, but others work with standard anodized parts. Regardless of whether the anodized surface is prepared according to a specialized process or a more standard process, there are many different processes that have been used to transfer an image to the metallic part. Some processes transfer images that are first applied to paper to the anodized surface by causing the ink resident on the paper to sublimate such that it flows into pores in the anoxic coating. One example of a modified anodizing technique that also uses sublimating inks is described in U.S. Pat. No. 4,451,335. In the process described in that patent an aluminum part is anodized in the presence of a polyhydric alcohol. The part is washed and dried, and an image is applied to the surface by subliming ink from a heat transfer sheet such as paper to the surface of the anodized part, which is heated.
Other examples of techniques according to which images are transferred on to anodized surfaces include screen printing, staining, and melting a variety of coloring compounds.
The techniques mentioned above are said to result in the initial transfer of high quality images, including multicolor images. However, the durability of the images produced according to these processes is fairly low, especially when the part is exposed to ultra violet light, which causes the images to fade, in some cases quite rapidly.
There is a need, therefore, for a method of applying multicolor images to anodized surfaces and to surfaces made of other materials.